Measurement method and apparatus

ABSTRACT

A method involving obtaining a simulation of a contour of a pattern to be formed on a substrate using a patterning process, determining a location of an evaluation point on the simulated contour of the pattern, the location spatially associated with a location of a corresponding evaluation point on a design layout for the pattern, and producing electronic information corresponding to a spatial bearing between the location of the evaluation point on the simulated contour and the location of the corresponding evaluation point on the design layout, wherein the information corresponding to the spatial bearing is configured for determining a location of an evaluation point on a measured image of at least part of the pattern, the evaluation point on the measured image spatially associated with the corresponding evaluation point on the design layout.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of U.S. application 62/515,921 whichwas filed on Jun. 6, 2017 and which is incorporated herein in itsentirety by reference.

FIELD

The present description relates to methods of, and apparatuses for,measurement.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.,including part of, one, or several dies) on a substrate (e.g., a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

SUMMARY

Manufacturing devices, such as semiconductor devices, typically involvesprocessing a substrate (e.g., a semiconductor wafer) using a number offabrication processes to form various features and multiple layers ofthe devices. Such layers and features are typically manufactured andprocessed using, e.g., deposition, lithography, etch,chemical-mechanical polishing, and ion implantation. Multiple devicesmay be fabricated on a plurality of dies on a substrate and thenseparated into individual devices. This device manufacturing process maybe considered a patterning process. A patterning process involves apatterning step, such as optical and/or nanoimprint lithography using alithographic apparatus, to provide a pattern on a substrate andtypically, but optionally, involves one or more related patternprocessing steps, such as resist development by a development apparatus,baking of the substrate using a bake tool, etching using the patternusing an etch apparatus, etc. Further, one or more metrology processesare typically involved in the patterning process.

Metrology processes are used at various steps during a patterningprocess to monitor and control the process. For example, metrologyprocesses are used to measure one or more characteristics of asubstrate, such as a relative location (e.g., registration, overlay,alignment, etc.) or dimension (e.g., line width, critical dimension(CD), thickness, etc.) of features formed on the substrate during thepatterning process, such that, for example, the performance of thepatterning process can be determined from the one or morecharacteristics. If the one or more characteristics are unacceptable(e.g., out of a predetermined range for the characteristic(s)), themeasurements of the one or more characteristics may be used to alter oneor more parameters of the patterning process such that furthersubstrates manufactured by the patterning process have an acceptablecharacteristic(s).

With the advancement of lithography and other patterning processtechnologies, the dimensions of functional elements have continuallybeen reduced while the amount of the functional elements, such astransistors, per device has been steadily increased over decades. In themeanwhile, the requirement of accuracy in terms of overlay, criticaldimension (CD), etc. has become more and more stringent. Errors, such asoverlay errors, CD errors, etc., will inevitably be produced in thepatterning process. For example, imaging errors may be produced fromoptical aberration, patterning device heating, patterning device errors,and/or substrate heating and can be characterized in terms of, e.g.,overlay errors, CD errors, etc. Additionally or alternatively, errorsmay be introduced in other parts of the patterning process, such as inetch, development, bake, etc. and similarly can be characterized interms of, e.g., overlay errors, CD errors, etc. The errors may directlycause a problem in terms of the function of the device, includingfailure of the device to function or one or more electrical problems ofthe functioning device.

As noted above, in patterning processes, it is desirable to frequentlymake measurements of the structures created, e.g., for process controland verification. One or more parameters of the structures are typicallymeasured or determined, for example the critical dimension of astructure, the overlay error between successive layers formed in or onthe substrate, etc. There are various techniques for making measurementsof the microscopic structures formed in a patterning process. Varioustools for making such measurements are known including, but not limitedto, scanning electron microscopes (SEMs), which are often used tomeasure critical dimension (CD). SEMs have high resolving power and arecapable of resolving features of the order of 30 nm or less, 20 nm orless, 10 nm or less, or 5 nm or less. SEM images of semiconductordevices are often used in the semiconductor fab to observe what ishappening at the device level.

The measurement information (such as extracted from SEM images of devicestructures) can be used for process modeling, existing model calibration(including recalibration), defect detection, estimation,characterization or classification, yield estimation, process control ormonitoring, etc.

In an embodiment, there is provided a method comprising: obtaining asimulation of a contour of a pattern to be formed on a substrate using apatterning process; determining, by a hardware computer system, alocation of an evaluation point on the simulated contour of the pattern,the location spatially associated with a location of a correspondingevaluation point on a design layout for the pattern; and producing, bythe hardware computer system, electronic information corresponding to aspatial bearing between the location of the evaluation point on thesimulated contour and the location of the corresponding evaluation pointon the design layout, wherein the information corresponding to thespatial bearing is configured for determining a location of anevaluation point on a measured image of at least part of the pattern,the evaluation point on the measured image spatially associated with thecorresponding evaluation point on the design layout.

In an embodiment, there is provided a method comprising: obtainingelectronic information corresponding to a spatial bearing between alocation of an evaluation point on a simulated contour of a pattern tobe formed on a substrate using a patterning process and a location of acorresponding evaluation point on a design layout for the pattern;obtaining a measured image of at least part of the pattern; determining,by a hardware computer system and based on the spatial bearinginformation, a location of an evaluation point on the measured image ofthe at least part of the pattern, the evaluation point on the measuredimage spatially associated with the corresponding evaluation point onthe design layout; and outputting spatial parameter information based onthe determined location.

In an aspect, there is provided a method of manufacturing deviceswherein a device pattern is applied to a series of substrates using apatterning process, the method including evaluating a patternedstructure formed using the patterning process using a method describedherein and controlling the patterning process for one or more of thesubstrates in accordance with the result of the method. In anembodiment, the patterned structure is formed on at least one of thesubstrates and the method comprises controlling the patterning processfor later substrates in accordance with the result of the method.

In aspect, there is provided a non-transitory computer program productcomprising machine-readable instructions configured to cause a processorto cause performance of a method described herein.

In an aspect, there is provided an inspection system. The systemincludes an inspection apparatus as described herein; and an analysisengine comprising a non-transitory computer program product as describedherein. In an embodiment, the inspection apparatus comprises an electronbeam inspection apparatus. In an embodiment, the system furthercomprises a lithographic apparatus comprising a support structureconfigured to hold a patterning device to modulate a radiation beam anda projection optical system arranged to project the modulated radiationbeam onto a radiation-sensitive substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, withreference to the accompanying drawings in which:

FIG. 1 schematically depicts an embodiment of a lithographic apparatus;

FIG. 2 schematically depicts an embodiment of a lithographic cell orcluster;

FIG. 3 schematically depicts an embodiment of a scanning electronmicroscope (SEM);

FIG. 4 schematically depicts an embodiment of an electron beaminspection apparatus;

FIG. 5 depicts an example flow chart for modeling and/or simulating atleast part of a patterning process;

FIG. 6 depicts an example flow chart for model calibration;

FIG. 7 schematically depicts an embodiment of a pattern analyzedaccording to an embodiment of a method;

FIG. 8 depicts an example flow chart for an evaluation point (EP)analysis method;

FIG. 9 schematically depicts an embodiment of a part of a patternanalyzed according to an embodiment of a method; and

FIG. 10 schematically depicts an embodiment of a part of a patternanalyzed according to an embodiment of a method.

DETAILED DESCRIPTION

Before describing embodiments in detail, it is instructive to present anexample environment in which embodiments may be implemented.

FIG. 1 schematically depicts a lithographic apparatus LA. The apparatuscomprises:

an illumination system (illuminator) IL configured to condition aradiation beam B (e.g. DUV radiation or EUV radiation);

a support structure (e.g. a mask table) MT constructed to support apatterning device (e.g. a mask) MA and connected to a first positionerPM configured to accurately position the patterning device in accordancewith certain parameters;

a substrate table (e.g. a wafer table) WTa constructed to hold asubstrate (e.g. a resist-coated wafer) W and connected to a secondpositioner PW configured to accurately position the substrate inaccordance with certain parameters; and

a projection system (e.g. a refractive projection lens system) PSconfigured to project a pattern imparted to the radiation beam B bypatterning device MA onto a target portion C (e.g. comprising one ormore dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The patterning device support structure holds the patterning device in amanner that depends on the orientation of the patterning device, thedesign of the lithographic apparatus, and other conditions, such as forexample whether or not the patterning device is held in a vacuumenvironment. The patterning device support structure can use mechanical,vacuum, electrostatic or other clamping techniques to hold thepatterning device. The patterning device support structure may be aframe or a table, for example, which may be fixed or movable asrequired. The patterning device support structure may ensure that thepatterning device is at a desired position, for example with respect tothe projection system. Any use of the terms “reticle” or “mask” hereinmay be considered synonymous with the more general term “patterningdevice.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam, which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.,employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g., employing a programmable mirror array of a typeas referred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore tables (e.g., two or more substrate table, two or more patterningdevice support structures, or a substrate table and metrology table). Insuch “multiple stage” machines the additional tables may be used inparallel, or preparatory steps may be carried out on one or more tableswhile one or more other tables are being used for pattern transfer.

The lithographic apparatus may also be of a type wherein at least aportion of the substrate may be covered by a liquid having a relativelyhigh refractive index, e.g., water, so as to fill a space between theprojection system and the substrate. An immersion liquid may also beapplied to other spaces in the lithographic apparatus, for example,between the mask and the projection system. Immersion techniques arewell known in the art for increasing the numerical aperture ofprojection systems. The term “immersion” as used herein does not meanthat a structure, such as a substrate, must be submerged in liquid, butrather only means that liquid is located between the projection systemand the substrate during exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDincluding, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may include an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL mayinclude various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross section.

The radiation beam B is incident on the patterning device (e.g., mask)MA, which is held on the patterning device support (e.g., mask tableMT), and is patterned by the patterning device. Having traversed thepatterning device (e.g., mask) MA, the radiation beam B passes throughthe projection system PS, which focuses the beam onto a target portion Cof the substrate W. With the aid of the second positioner PW andposition sensor IF (e.g., an interferometric device, linear encoder, 2-Dencoder or capacitive sensor), the substrate table WTa can be movedaccurately, e.g., so as to position different target portions C in thepath of the radiation beam B. Similarly, the first positioner PM andanother position sensor (which is not explicitly depicted in FIG. 1) canbe used to accurately position the patterning device (e.g., mask) MAwith respect to the path of the radiation beam B, e.g., after mechanicalretrieval from a mask library, or during a scan. In general, movement ofthe patterning device support (e.g., mask table) MT may be realized withthe aid of a long-stroke module (coarse positioning) and a short-strokemodule (fine positioning), which form part of the first positioner PM.Similarly, movement of the substrate table WTa may be realized using along-stroke module and a short-stroke module, which form part of thesecond positioner PW. In the case of a stepper (as opposed to a scanner)the patterning device support (e.g., mask table) MT may be connected toa short-stroke actuator only, or may be fixed.

Patterning device (e.g., mask) MA and substrate W may be aligned usingmask alignment marks M1, M2 and substrate alignment marks P1, P2.Although the substrate alignment marks as illustrated occupy dedicatedtarget portions, they may be located in spaces between target portions(these are known as scribe-lane alignment marks). Similarly, insituations in which more than one die is provided on the patterningdevice (e.g., mask) MA, the mask alignment marks may be located betweenthe dies. Small alignment markers may also be included within dies, inamongst the device features, in which case it is desirable that themarkers be as small as possible and not require any different patterningor other process conditions than adjacent features. An embodiment of analignment system, which detects the alignment markers, is describedfurther below.

The depicted apparatus could be used in at least one of the followingmodes:

In step mode, the patterning device support (e.g., mask table) MT andthe substrate table WTa are kept essentially stationary, while an entirepattern imparted to the radiation beam is projected onto a targetportion C at one time (i.e., a single static exposure). The substratetable WTa is then shifted in the X and/or Y direction so that adifferent target portion C can be exposed. In step mode, the maximumsize of the exposure field limits the size of the target portion Cimaged in a single static exposure.

In scan mode, the patterning device support (e.g., mask table) MT andthe substrate table WTa are scanned synchronously while a patternimparted to the radiation beam is projected onto a target portion C(i.e., a single dynamic exposure). The velocity and direction of thesubstrate table WTa relative to the patterning device support (e.g.,mask table) MT may be determined by the (de-)magnification and imagereversal characteristics of the projection system PS. In scan mode, themaximum size of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

In another mode, the patterning device support (e.g., mask table) MT iskept essentially stationary holding a programmable patterning device,and the substrate table WTa is moved or scanned while a pattern impartedto the radiation beam is projected onto a target portion C. In thismode, generally a pulsed radiation source is employed and theprogrammable patterning device is updated as required after eachmovement of the substrate table WTa or in between successive radiationpulses during a scan. This mode of operation can be readily applied tomaskless lithography that utilizes programmable patterning device, suchas a programmable mirror array of a type as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

Lithographic apparatus LA is of a so-called dual stage type which hastwo tables WTa, WTb (e.g., two substrate tables) and two stations—anexposure station and a measurement station—between which the tables canbe exchanged. For example, while a substrate on one table is beingexposed at the exposure station, another substrate can be loaded ontothe other substrate table at the measurement station and variouspreparatory steps carried out. The preparatory steps may include mappingthe surface control of the substrate using a level sensor LS andmeasuring the position of alignment markers on the substrate using analignment sensor AS, both sensors being supported by a reference frameRF. If the position sensor IF is not capable of measuring the positionof a table while it is at the measurement station as well as at theexposure station, a second position sensor may be provided to enable thepositions of the table to be tracked at both stations. As anotherexample, while a substrate on one table is being exposed at the exposurestation, another table without a substrate waits at the measurementstation (where optionally measurement activity may occur). This othertable has one or more measurement devices and may optionally have othertools (e.g., cleaning apparatus). When the substrate has completedexposure, the table without a substrate moves to the exposure station toperform, e.g., measurements and the table with the substrate moves to alocation (e.g., the measurement station) where the substrate is unloadedand another substrate is load. These multi-table arrangements enable asubstantial increase in the throughput of the apparatus.

As shown in FIG. 2, a lithographic apparatus LA may form part of alithographic cell LC, also sometimes referred to as a lithocell orlithocluster, which also includes apparatus to perform one or more pre-and post-pattern transfer processes on a substrate. Conventionally theseinclude one or more spin coaters SC to deposit a resist layer, one ormore developers DE to develop patterned resist, one or more chill platesCH and one or more bake plates BK. A substrate handler, or robot, ROpicks up a substrate from input/output ports I/O1, I/O2, moves itbetween the different process devices and delivers it to the loading bayLB of the lithographic apparatus. These devices, which are oftencollectively referred to as the track, are under the control of a trackcontrol unit TCU which is itself controlled by the supervisory controlsystem SCS, which also controls the lithographic apparatus vialithographic control unit LACU. Thus, the different apparatus may beoperated to maximize throughput and processing efficiency.

To enable that the substrate that is processed (e.g., exposed) by thepatterning process is processed correctly and consistently, it isdesirable to inspect a processed substrate to measure one or moreproperties such as overlay error between subsequent layers, linethickness, critical dimension (CD), etc. If an error is detected, anadjustment may be made to the patterning process, e.g., in terms ofchanging a design of, or changing a tool for designing, the patterningprocess, controlling an executing patterning process, etc.

An inspection apparatus can be used for such measurement. An inspectionapparatus is used to determine one or more properties of a substrate,and in particular, how one or more properties of different substrates ordifferent layers of the same substrate vary from layer to layer and/oracross a substrate and/or across different substrates, e.g., fromsubstrate to substrate. The inspection apparatus may be integrated intothe lithographic apparatus LA or the lithocell LC or may be astand-alone device.

An inspection apparatus to determine one or more properties of asubstrate can take various different forms. For example, the inspectionapparatus may use photon electromagnetic radiation to illuminate thesubstrate and detect radiation redirected by the substrate; suchinspection apparatuses may be referred to as bright-field inspectionapparatuses. A bright-field inspection apparatus may use radiation witha wavelength in, for example, the range of 150-900 nm. The inspectionapparatus may be image-based, i.e., taking an image of the substrate,and/or diffraction-based, i.e., measuring intensity of diffractedradiation. The inspection apparatus may inspect product features (e.g.,features of an integrated circuit to be formed using the substrate orfeatures of a mask) and/or inspect specific measurement targets (e.g.,overlay targets, focus/dose targets, CD gauge patterns, etc.).

Inspection of, e.g., semiconductor wafers is often done withoptics-based sub-resolution tools (bright-field inspection). But, insome cases, certain features to be measured are too small to beeffectively measured using bright-field inspection. For example,bright-field inspection of defects in features of a semiconductor devicecan be challenging. Moreover, as time progresses, features that arebeing made using patterning processes (e.g., semiconductor features madeusing lithography) are becoming smaller and in many cases, the densityof features is also increasing. Accordingly, a higher resolutioninspection technique is used and desired. An example inspectiontechnique is electron beam inspection. Electron beam inspection involvesfocusing a beam of electrons on a small spot on the substrate to beinspected. An image is formed by providing relative movement between thebeam and the substrate (hereinafter referred to as scanning the electronbeam) over the area of the substrate inspected and collecting secondaryand/or backscattered electrons with an electron detector. The image datais then processed to, for example, identify defects.

So, in an embodiment, the inspection apparatus may be an electron beaminspection apparatus (e.g., the same as or similar to a scanningelectron microscope (SEM)) that yields an image of a structure (e.g.,some or all the structure of a device, such as an integrated circuit)exposed or transferred on the substrate. FIG. 3 schematically depicts anembodiment of an electron beam inspection apparatus 200. A primaryelectron beam 202 emitted from an electron source 201 is converged bycondenser lens 203 and then passes through a beam deflector 204, an E×Bdeflector 205, and an objective lens 206 to irradiate a substrate 100 ona substrate table 101 at a focus.

When the substrate 100 is irradiated with electron beam 202, secondaryelectrons are generated from the substrate 100. The secondary electronsare deflected by the E x B deflector 205 and detected by a secondaryelectron detector 207. A two-dimensional electron beam image can beobtained by detecting the electrons generated from the sample insynchronization with, e.g., two dimensional scanning of the electronbeam by beam deflector 204 or with repetitive scanning of electron beam202 by beam deflector 204 in an X or Y direction, together withcontinuous movement of the substrate 100 by the substrate table 101 inthe other of the X or Y direction. Thus, in an embodiment, the electronbeam inspection apparatus has a field of view for the electron beamdefined by the angular range into which the electron beam can beprovided by the electron beam inspection apparatus (e.g., the angularrange through which the deflector 204 can provide the electron beam202). Thus, the spatial extent of the field of the view is the spatialextent to which the angular range of the electron beam can impinge on asurface (wherein the surface can be stationary or can move with respectto the field).

A signal detected by secondary electron detector 207 is converted to adigital signal by an analog/digital (A/D) converter 208, and the digitalsignal is sent to an image processing system 300. In an embodiment, theimage processing system 300 may have memory 303 to store all or part ofdigital images for processing by a processing unit 304. The processingunit 304 (e.g., specially designed hardware or a combination of hardwareand software or a computer readable medium comprising software) isconfigured to convert or process the digital images into datasetsrepresentative of the digital images. In an embodiment, the processingunit 304 is configured or programmed to cause execution of a methoddescribed herein. Further, image processing system 300 may have astorage medium 301 configured to store the digital images andcorresponding datasets in a reference database. A display device 302 maybe connected with the image processing system 300, so that an operatorcan conduct necessary operation of the equipment with the help of agraphical user interface.

FIG. 4 schematically illustrates a further embodiment of an inspectionapparatus. The system is used to inspect a sample 90 (such as asubstrate) on a sample stage 88 and comprises a charged particle beamgenerator 81, a condenser lens module 82, a probe forming objective lensmodule 83, a charged particle beam deflection module 84, a secondarycharged particle detector module 85, and an image forming module 86.

The charged particle beam generator 81 generates a primary chargedparticle beam 91. The condenser lens module 82 condenses the generatedprimary charged particle beam 91. The probe forming objective lensmodule 83 focuses the condensed primary charged particle beam into acharged particle beam probe 92. The charged particle beam deflectionmodule 84 scans the formed charged particle beam probe 92 across thesurface of an area of interest on the sample 90 secured on the samplestage 88. In an embodiment, the charged particle beam generator 81, thecondenser lens module 82 and the probe forming objective lens module 83,or their equivalent designs, alternatives or any combination thereof,together form a charged particle beam probe generator which generatesthe scanning charged particle beam probe 92.

The secondary charged particle detector module 85 detects secondarycharged particles 93 emitted from the sample surface (maybe also alongwith other reflected or scattered charged particles from the samplesurface) upon being bombarded by the charged particle beam probe 92 togenerate a secondary charged particle detection signal 94. The imageforming module 86 (e.g., a computing device) is coupled with thesecondary charged particle detector module 85 to receive the secondarycharged particle detection signal 94 from the secondary charged particledetector module 85 and accordingly forming at least one scanned image.In an embodiment, the secondary charged particle detector module 85 andimage forming module 86, or their equivalent designs, alternatives orany combination thereof, together form an image forming apparatus whichforms a scanned image from detected secondary charged particles emittedfrom sample 90 being bombarded by the charged particle beam probe 92.

In an embodiment, a monitoring module 87 is coupled to the image formingmodule 86 of the image forming apparatus to monitor, control, etc. thepatterning process and/or derive a parameter for patterning processdesign, control, monitoring, etc. using the scanned image of the sample90 received from image forming module 86. So, in an embodiment, themonitoring module 87 is configured or programmed to cause execution of amethod described herein. In an embodiment, the monitoring module 87comprises a computing device. In an embodiment, the monitoring module 87comprises a computer program to provide functionality herein and encodedon a computer readable medium forming, or disposed within, themonitoring module 87.

In an embodiment, like the electron beam inspection tool of FIG. 3 thatuses a probe to inspect a substrate, the electron current in the systemof FIG. 4 is significantly larger compared to, e.g., a CD SEM such asdepicted in FIG. 3, such that the probe spot is large enough so that theinspection speed can be fast. However, the resolution may not be as highas compared to a CD SEM because of the large probe spot.

The SEM images, from, e.g., the system of FIG. 3 and/or FIG. 4, may beprocessed to extract contours that describe the edges of objects,representing device structures, in the image. These contours are thentypically quantified via metrics, such as CD, at user-defined cut-lines.Thus, typically, the images of device structures are compared andquantified via metrics, such as an edge-to-edge distance (CD) measuredon extracted contours or simple pixel differences between images.

Now, besides measuring substrates in a patterning process, it is oftendesirable to use one or more tools to produce results that, for example,can be used to design, control, monitor, etc. the patterning process. Todo this, there may be provided one or more tools used in computationallycontrolling, designing, etc. one or more aspects of the patterningprocess, such as the pattern design for a patterning device (including,for example, adding sub-resolution assist features or optical proximitycorrections), the illumination for the patterning device, etc.Accordingly, in a system for computationally controlling, designing,etc. a manufacturing process involving patterning, the majormanufacturing system components and/or processes can be described byvarious functional modules. In particular, in an embodiment, one or moremathematical models can be provided that describe one or more stepsand/or apparatuses of the patterning process, including typically thepattern transfer step. In an embodiment, a simulation of the patterningprocess can be performed using one or more mathematical models tosimulate how the patterning process forms a patterned substrate using ameasured or design pattern provided by a patterning device.

An exemplary flow chart for modeling and/or simulating parts of apatterning process (e.g., lithography in a lithographic apparatus) isillustrated in FIG. 5. As will be appreciated, the models may representa different patterning process and need not comprise all the modelsdescribed below. A source model 500 represents optical characteristics(including radiation intensity distribution, bandwidth and/or phasedistribution) of the illumination of a patterning device. The sourcemodel 500 can represent the optical characteristics of the illuminationthat include, but not limited to, numerical aperture settings,illumination sigma (σ) settings as well as any particular illuminationshape (e.g. off-axis radiation shape such as annular, quadrupole,dipole, etc.), where σ (or sigma) is outer radial extent of theilluminator.

A projection optics model 510 represents optical characteristics(including changes to the radiation intensity distribution and/or thephase distribution caused by the projection optics) of the projectionoptics. The projection optics model 510 can represent the opticalcharacteristics of the projection optics, including aberration,distortion, one or more refractive indexes, one or more physical sizes,one or more physical dimensions, etc.

The patterning device model module 120 captures how the design featuresare laid out in the pattern of the patterning device and may include arepresentation of detailed physical properties of the patterning device,as described, for example, in U.S. Pat. No. 7,587,704. The objective ofthe simulation is to accurately predict, for example, edge placementsand CDs, which can then be compared against the device design. Thedevice design is generally defined as the pre-OPC patterning devicelayout, and will be provided in a standardized digital file format suchas GDSII or OASIS.

A design layout model 520 represents optical characteristics (includingchanges to the radiation intensity distribution and/or the phasedistribution caused by a given design layout) of a design layout (e.g.,a device design layout corresponding to a feature of an integratedcircuit, a memory, an electronic device, etc.), which is therepresentation of an arrangement of features on or formed by thepatterning device. The design layout model 520 can represent one or morephysical properties of a physical patterning device, as described, forexample, in U.S. Pat. No. 7,587,704, which is incorporated by referencein its entirety. Since the patterning device used in the lithographicprojection apparatus can be changed, it is desirable to separate theoptical properties of the patterning device from the optical propertiesof the rest of the lithographic projection apparatus including at leastthe illumination and the projection optics.

An aerial image 530 can be simulated from the source model 500, theprojection optics model 510 and the design layout model 520. An aerialimage (AI) is the radiation intensity distribution at substrate level.Optical properties of the lithographic projection apparatus (e.g.,properties of the illumination, the patterning device and the projectionoptics) dictate the aerial image.

A resist layer on a substrate is exposed by the aerial image and theaerial image is transferred to the resist layer as a latent “resistimage” (RI) therein. The resist image (RI) can be defined as a spatialdistribution of solubility of the resist in the resist layer. A resistimage 550 can be simulated from the aerial image 530 using a resistmodel 540. The resist model can be used to calculate the resist imagefrom the aerial image, an example of which can be found in U.S. PatentApplication Publication No. US 2009-0157360, the disclosure of which ishereby incorporated by reference in its entirety. The resist modeltypically describes the effects of chemical processes which occur duringresist exposure, post exposure bake (PEB) and development, in order topredict, for example, contours of resist features formed on thesubstrate and so it typically related only to such properties of theresist layer (e.g., effects of chemical processes which occur duringexposure, post-exposure bake and development). In an embodiment, theoptical properties of the resist layer, e.g., refractive index, filmthickness, propagation and polarization effects—may be captured as partof the projection optics model 510.

So, in general, the connection between the optical and the resist modelis a simulated aerial image intensity within the resist layer, whicharises from the projection of radiation onto the substrate, refractionat the resist interface and multiple reflections in the resist filmstack. The radiation intensity distribution (aerial image intensity) isturned into a latent “resist image” by absorption of incident energy,which is further modified by diffusion processes and various loadingeffects. Efficient simulation methods that are fast enough for full-chipapplications approximate the realistic 3-dimensional intensitydistribution in the resist stack by a 2-dimensional aerial (and resist)image.

In an embodiment, the resist image can be used an input to apost-pattern transfer process model module 150. The post-patterntransfer process model 150 defines performance of one or morepost-resist development processes (e.g., etch, development, etc.).

Simulation of the patterning process can, for example, predict contours,CDs, edge placement (e.g., edge placement error), etc. in the resistand/or etched image. Thus, the objective of the simulation is toaccurately predict, for example, edge placement, and/or aerial imageintensity slope, and/or CD, etc. of the printed pattern. These valuescan be compared against an intended design to, e.g., correct thepatterning process, identify where a defect is predicted to occur, etc.The intended design is generally defined as a pre-OPC design layoutwhich can be provided in a standardized digital file format such asGDSII or OASIS or other file format.

Thus, the model formulation describes most, if not all, of the knownphysics and chemistry of the overall process, and each of the modelparameters desirably corresponds to a distinct physical or chemicaleffect. The model formulation thus sets an upper bound on how well themodel can be used to simulate the overall manufacturing process.

An application of the one or more models described herein insophisticated fine-tuning steps of the patterning process, such asfine-tuning steps applied to the illumination, projection system and/orpatterning device design. These include, for example, but not limitedto, optimization of numerical aperture, optimization of coherencesettings, customized illumination schemes, use of phase shiftingfeatures in or on a patterning device, optical proximity correction inthe patterning device layout, placement of sub-resolution assistfeatures in the patterning device layout or other methods generallydefined as “resolution enhancement techniques” (RET).

As an example, optical proximity correction (OPC) addresses the factthat the final size and placement of a printed feature on the substratewill not simply be a function of the size and placement of thecorresponding feature on the patterning device. For the small featuresizes and high feature densities present on typical electronic devicedesigns, the position of a particular edge of a given feature will beinfluenced to a certain extent by the presence or absence of otheradjacent features. In an embodiment, these proximity effects arise fromcoupling of radiation from more than one feature. In an embodiment,proximity effects arise from diffusion and other chemical effects duringpost-exposure bake (PEB), resist development, and etching that generallyfollow lithographic exposure.

In order to help ensure that the features are generated on a substratein accordance with the requirements of the given device design,proximity effects should be predicted utilizing sophisticated numericalmodels, and corrections or pre-distortions are applied to the design ofthe patterning device before successful manufacturing of devices becomespossible. These modifications may include shifting or biasing of edgepositions or line widths and/or application of one or more assistfeatures that are not intended to print themselves, but will affect theproperties of an associated primary feature.

The application of a model-based patterning process design requires goodprocess models and considerable computational resources, given the manymillions of features typically present in a chip design. However,applying model-based design is generally not an exact science, but aniterative process that does not always resolve all possible weaknessesof a device design. Therefore, post-OPC designs, i.e. patterning devicelayouts after application of all pattern modifications by OPC and anyother RET's, should be verified by design inspection, e.g., intensivefull-chip simulation using calibrated numerical process models, in orderto reduce the possibility of design flaws being built into themanufacturing of a patterning device.

However, sometimes the model parameters may be inaccurate from, e.g.,measurement and reading errors, and/or there may be other imperfectionsin the system. With precise calibration of the model parameters,extremely accurate simulations can be done. So, since computationalpatterning process evaluation should involve robust models that describethe patterning process precisely, a calibration procedure for suchmodels should be used to achieve models that are valid, robust andaccurate across the applicable process window.

To enable calibration of the computational models (and optionally inorder that the substrate that is exposed by the lithographic apparatusis exposed correctly and consistently), it is desirable to take variousmeasurements of patterns printed on a substrate using an inspectionapparatus. In some embodiments, the inspection apparatus may be ascanning electron microscope (SEM) that yields an image of one or morestructures (e.g., one or more test (or calibration) patterns or one ormore patterns corresponding to some or all the structures of a device)exposed or transferred on the substrate.

So, in an embodiment, calibration is done by printing a certain numberof 1-dimensional and/or 2-dimensional gauge patterns on a substrate(e.g., the gauge patterns may be specially designated measurementpatterns or may be device parts of a design device pattern as printed onthe substrate) and performing measurements on the printed patterns. Morespecifically, those 1-dimensional gauge patterns are line-space patternswith varying pitch and CD, and the 2-dimensional gauge patternstypically include line-ends, contacts, and/or SRAM (Static Random AccessMemory) patterns. These patterns are then imaged onto a substrate andresulting substrate CDs or contact hole (also known as a via orthrough-chip via) energy are measured. The original gauge patterns andtheir substrate measurements are then used jointly to determine themodel parameters which reduce or minimize the difference between modelpredictions and substrate measurements. In an embodiment, the one ormore gauge or calibration patterns may not correspond to structures in adevice. But, the one or more gauge or calibration patterns possessenough similarities with one or more patterns in the device to allowaccurate prediction of the one or more device patterns.

An example model calibration process as described above is illustratedin FIG. 6. The process begins with a design layout 600, which caninclude gauge and optionally other test patterns, which can be in astandard format such as GDSII or OASIS. Next, the design layout is usedto generate a patterning device layout at 610, which can be in astandard format such as GDSII or OASIS and which may include OPC orother RET features. Then, in an embodiment, two separate paths aretaken, for simulation and measurement.

In a simulation path, the patterning device layout and a model 620 areused to create a simulated resist image in step 630. The model 620provides a model of the patterning process for use in computationallithography, and the calibration process aims to make the model 620 asaccurate as possible, so that computational lithography results arelikewise accurate. The simulated resist image is then used to determinepredicted critical dimensions (CDs), etc. in step 640.

In a measurement path, the patterning device layout 610 is used with orto form a physical mask (e.g., a reticle), which is then imaged onto asubstrate at 650. The patterning process (e.g. NA, focus, dose,illumination source, etc. for optical lithography) used to pattern thesubstrate is the same as that intended to be captured in model 620.Measurements (e.g. using a metrology tool (such as a SEM, etc.) are thenperformed on the actual patterned substrate at 660, which yieldsmeasured CDs, contours, etc.

A comparison is made at 670 between the measurements from 660 and thepredictions from 640. If the comparison determines that the predictionsmatch the measurements within a predetermined error threshold, the modelis considered to be successfully calibrated at 690. Otherwise, changesare made to the model 620, and steps 630, 640 and 670 are repeated untilthe predictions generated using the model 620 match the measurementswithin a predetermined threshold. In an embodiment, the model comprisesan OPC model. While the description hereafter will focus on an OPC modelas an embodiment, the model may be other than or in addition to an OPCmodel.

As noted above, values of a geometric parameter (such as CD) areextracted from an image (e.g., an image generated using an electron beamsuch as a SEM image) of a formed pattern on a substrate for, e.g. modelcalibration or for other purposes. For example, as noted above for modelcalibration, a gauge pattern can be used.

Referring to FIG. 7, a schematic of a pattern (e.g., a gauge pattern) invarious forms is depicted. FIG. 7 illustrates an image of a generallyelliptical pattern 720 that is produced on a substrate from, e.g., anominally rectangular design layout 700 (e.g., as designed to beproduced at the substrate). While the boundary of the generallyelliptical pattern 720 is depicted as a contour, it need not be acontour but rather the boundary can be the pixel data that representsthe edge of the pattern 720 (that is a contour has not been extracted).Further, the pattern in FIG. 7 is an elliptical shape that protrudesfrom the substrate wherein the interior of the pattern 720 is higherthan points immediately outside the boundary. However, the pattern 720need not be a protrusion but could be a trench type structure; in whichcase, the interior of the pattern 720 is below the region immediatelyexterior of the boundary of pattern 720. If pattern 720 were a trench,the nominally rectangular design layout 700 may be smaller and generallyin the interior of the pattern 720.

In an image of the pattern, gauges are specified and evaluated. In anembodiment, the gauges are the evaluation locations on the pattern todetermine values of a geometric parameter such as CD, edge position,etc. The values of the gauges can be used for various purposes indesign, control, etc. of a patterning process, an apparatus of thepatterning process or a tool used with design, control, etc. of apatterning process. In one particular example, the values of gauges areused for calibration of, for example, an OPC model. So, in that case,the calibration of an OPC model is effectively aiming to create a modelthat minimizes an error associated with the gauges. While an embodimentof the determination of gauge values for model calibration is describedhere specifically, it will be appreciated that the determination ofgauge values can be used for various purposes.

In FIG. 7, an example gauge is illustrated as imaginary line 770 that issuperimposed on the boundary (e.g., contour) of a shape of the patternthat is measured, i.e., the gauge 770 for CD in the X direction. As willbe appreciated, numerous other gauges can be specified (e.g., moregauges in the X direction and gauges in the Y direction). Gauge 770 issometimes referred to as a cutline and so facilitates the measurementdistance of a selected “cut” on the pattern. The cutline is typicallyaligned in the X and/or Y direction and in some cases a certain angle.Another example gauge is an evaluation point (EP) 760. An EP 760 doesnot necessarily require another corresponding point on a line like acutline. A gauge 770 or an EP 760 is normally collected from a substratepattern contour (i.e., the pattern image is processed to create acontour and then the edge position at the EP is extracted from thecontour at the desired EP).

The gauges are positioned at specific spots in a pattern layout andessentially represent the points at the boundary of the pattern.Desirably, a number of gauges are selected to be representative of theshape of the pattern but the number of gauges are limited by, e.g.,throughput concerns and diminishing returns (e.g., while more gaugeswill provide greater accuracy, it may not provide much more). Indeed,thousands of different measurements and/or shapes are made for any givenOPC model, so there is a variety of shapes present on any substrate thatare measured and all of them should be measured well if they are toreport values that correspond to what the actual OPC model would like tohave as far as information corresponding to the gauge positions.

As model calibration is done per edge around the pattern design layout(e.g., a polygon), for advanced technology nodes, evaluation points(EPs) can provide more comprehensive sampling of the pattern boundarythan cutlines and thus enable improvement in model calibration. As notedabove, evaluation of the EP and/or gauge typically involves extractionof the contour of the pattern from the image of the pattern (e.g., usingtechniques of contour extraction known in the art), which contour isable to represent the substrate pattern.

However, contour extraction can introduce artifacts and/or errors sincethe algorithms to extract the contour may not perfectly determine thecontour around the entirety of the shape of the pattern. Such artifactsand/or errors can impact the model accuracy. Similarly, smoothingtechniques applied to the contour can similarly introduce artifactsand/or errors.

Additionally or alternatively, to improve the quality of the contourextraction, the substrate pattern image quality should be high and somore image frames of the pattern can be captured and averaged togetherto obtain the higher quality pattern image from which the contour isextracted. Unfortunately, the more frames that are captured the more thesubstrate pattern is damaged by the incident electron beam radiation.This leads to additional error due to determining a contour from animage comprising data from a significantly damaged pattern feature.

Additionally or alternatively, the contour is typically constructed withmany more location points around the pattern boundary than what isrequired for EP sampling per pattern. For example, the contour istypically extracted for the entire pattern boundary. But, even withthose extra available location points, often interpolation is stillneeded to provide desired EP locations because the contour locationpoints may not correspond to all the desired EP locations.

Therefore, the contour extraction for EP gauge evaluation can result ina large contour data file, long computational time for contourextraction and/or EP positional error due to, for example,artifacts/errors in contour extraction and/or from interpolation.

So it is desired to provide an improved technique for determining EPlocations on a pattern image and obtaining the values of a geometricparameter at EP locations.

In an embodiment, a simulated contour of a pattern under consideration(and that is generated using, e.g., a design layout of the pattern) isused to effectively pre-generate EP locations. Then, the pre-generatedEP locations are used to identify the associated EP locations on animage of at least part of the formed pattern. In an embodiment, theimage EP locations are determined without extraction of a contour fromthe image. In an embodiment, data related to the pre-generated EPlocations are used to guide measurement of the image of the pattern.From the image EP locations, spatial positions or dimensions associatedwith the EPs at the image EP locations can be determined from the image.

In an embodiment, an inspection tool (such as an electron beaminspection apparatus) measures the EPs (e.g., determines their spatialposition in a coordinate system or measures a dimension associated them)according the pre-generated EP locations from the image, e.g., directlywithout contour extraction or with reduced contour extraction. In anembodiment, the inspection apparatus can do image measurement ineffectively real-time per image and so there would be no additionalthroughput impact on top of the imaging time. In an embodiment, thethroughput can be reduced by not having to perform a contour extractionor a contour extraction only at one or more select portions.Additionally or alternatively, by direct measurement on an image (i.e.,measurement on the image without contour extraction of the partmeasured), fewer image frames of the pattern may be required compared tothe number of image frames needed for contour extraction and themeasurement can be closer to the real pattern (i.e., less damage to thepattern than would otherwise be required to obtain the larger number ofimage frames for contour extraction). Additionally or alternatively,image acquisition throughput could be significantly improved as fewerimage frames may need to be captured (particularly for large imagesand/or a large number of patterns).

FIG. 8 is a flow chart of an embodiment of a method of determining EPlocations on a pattern image and obtaining the values of a geometricparameter at the EP locations. At 800, a simulated target contour of apattern is obtained at one or more nominal processing conditions of thepatterning process used to produce the pattern on a substrate. In anembodiment, the simulated target contour is determined based on a designlayout for the pattern as formed on the substrate. In an embodiment, thedesign layout is in the form of a polygon; in that case, the designlayout would be a target polygon. While an embodiment will be describedin relation to a target polygon, the embodiments are generallyapplicable to any design layout for the pattern. In an embodiment, asimulation is run to obtain the simulated target contour. In anembodiment, a simulation model as described with respect to FIG. 5 canbe used.

Referring to back to FIG. 7, a schematic example of a simulated targetcontour is depicted along with a target polygon. As seen in FIG. 7, atarget polygon 700 is depicted along with a simulated target contour710. As will be appreciated, a formed pattern will typically not matchthe target polygon exactly and that is shown here by the rounding of thesimulated target contour compared to the target polygon Further, theformed pattern often may not have the same cross-sectional dimensions asthe target polygon and that is shown here by the shrinking of thesimulated target contour compared to the target polygon. As will beappreciated, the simulated target contour need not be rounded asschematically depicted and/or need not have smaller cross-sectionaldimensions.

The target polygon will have one or more EPs located on or at the targetpolygon boundary. Typically, there will be a plurality of EPs specifiedalong the target polygon boundary. The locations of the EPs for thetarget polygon can be selected by the user or be automaticallydetermined. In an embodiment, a plurality of EPs can be specifieduniformly along the boundary of the target polygon. In an embodiment, anEP can be specified for at least corner of the polygon. In anembodiment, an EP can be specified for each corner of a target polygon.In an embodiment, a greater concentration of EPs is specified for acorner than along a straight portion of the polygon. In an embodiment,the number of EPs specified for a target polygon is 5 or more, 10 ormore, 20 or more, or 50 or more.

Having the simulated target contour and the target polygon, at 810, thelocations on the nominal simulated target contour of one or more EPs aredetermined based on the target polygon. That is, one or more EPs aredefined with respect to the target polygon and a corresponding EPlocation is determined on the simulated target contour for each such EPdefined with respect to the target polygon. For example, as shown inFIG. 7, one or more EPs 730 are defined on the target polygon 700 andfor each EP 730, there is determined a EP location 740 on the simulatedtarget contour 710. While 3 sets of corresponding EP 730 and EP 740 aremarked in FIG. 7, further example sets of corresponding EP on the targetpolygon and on the simulated target contour are shown in FIG. 7.

Imaginary line 750 helps to depict the spatial relationship between thelocations of EP 730 and EP 740. In an embodiment, the location of EP 740corresponding to an associated EP 730 is the nearest location on thesimulated target contour 710 to the location of EP 730. That is, asubstantially shortest distance is found between an EP 730 and thesimulated target contour 710 and that location becomes the location ofEP 740. Thus, in an embodiment, the portion of line 750 between EP 730and EP 740 is a substantially shortest distance. In an embodiment, thesubstantially shortest distance can be selected from the range of 90% ofthe shortest distance to 110% of the shortest distance. In anembodiment, the location of EP 740 corresponds to the location on thesimulated target contour 710 at which an imaginary line (e.g., line 750)that is substantially perpendicular to a tangent to, or that issubstantially perpendicular to the side of, a portion of the simulatedtarget contour 710 nearest to the EP 730 runs through EP 730. In anembodiment, substantially perpendicular can be selected from 80° to110°.

So, the determined location of EP 740 from associated EP 730 establishesa spatial bearing between the locations of EP 730 and 740. The imaginaryline 750 helps depict this spatial bearing. As will be described infurther detail below, the location of an EP 760 on a measured image ofthe pattern will be determined using this spatial bearing by, e.g.,locating the periphery of the measured pattern image along this spatialbearing.

At 820, information regarding the spatial bearing is produced for use indetermining the location of an EP on a measured pattern image. So, in anembodiment, for each EP of interest defined with respect to the targetpolygon, there is provided electronic information regarding the spatialbearing for that EP. In an embodiment, the information is specified forthe coordinate system of the measured pattern image. In an embodiment,the information is specified in the GDS, GDSII or OASIS coordinatesystem. In an embodiment, the information is specified in the coordinatesystem of the inspection apparatus for the image. Where necessary, in anembodiment, the information regarding the spatial bearing comprisesidentifying information regarding the pattern to enable an inspectionapparatus to locate the pattern (to which the EP information is related)as formed on the substrate or to locate that pattern in an image of thesubstrate comprising the pattern.

In an embodiment, the information regarding the spatial bearingcomprises the location of each EP 730 and associated EP 740. Using thelocations of EP 730 and EP 740, a spatial bearing direction can becalculated. In an embodiment, the spatial bearing direction comprises anangle, a slope or other representation of direction. In an embodiment,the information comprises the location of EP 730 and/or of EP 740 and aspatial bearing direction (e.g., angle). An example of the spatialbearing direction is shown as angle θ in FIG. 7.

At 830, an image of the pattern formed on a substrate by the patterningprocess at the nominal conditions is obtained. In an embodiment, theimage is obtained by measurement with an electron beam. In anembodiment, the image is a SEM image. In an embodiment, prior toobtaining a value of a geometric parameter from the image for an EP, theimage is aligned with the coordinate system of the target polygon (e.g.,target polygon 700) and/or the simulated contour of the pattern (e.g.,simulated target contour 710). In an embodiment, prior to obtaining avalue of a geometric parameter from the image for an EP, the image isaligned with the GDS, GDSII or OASIS coordinate system, which can bedone by Die to Database (D2DB) functionality of, e.g., an inspectionapparatus.

In an embodiment, obtaining the image comprises measuring a formedpattern on the substrate using an inspection apparatus (such as anapparatus as described with respect to FIG. 3 and/or 4). In anembodiment, the measuring of the formed pattern is guided by theinformation regarding the spatial bearing. That is an embodiment thepattern is specially measured at regions along the spatial bearingdirection corresponding to each of the one or more EPs for which spatialbearing information is provided. For example, the location of EP 730and/or of EP 740 with respect to associated formed pattern can bedetermined, if necessary, in the coordinate system of the inspectionapparatus and then a measurement can be taken within a thresholddistance from that location of EP 730 and/or of EP 740 with respect tothe formed pattern and along the spatial bearing direction (which can bedetermined, by, e.g., the inspection apparatus, from the informationregarding the locations of EP 730 and EP 740 or which be included withthe spatial bearing information). In an embodiment, the guidedmeasurement comprises the inspection apparatus obtaining extrameasurement information at the regions of the pattern. In an embodiment,the guided measurement comprises the inspection apparatus obtainingmeasurement information at the regions of the pattern but not at otherlocations on the pattern.

At 840, a determination of the location of one or more EPs on themeasured pattern image is performed. If necessary, the image is alignedwith the coordinate system of the spatial bearing information, e.g.,with the GDS, GDSII or OASIS coordinate system, or with a simulatedpattern contour (e.g., by a computer image processing technique that canmathematically align the simulated target contour with the generalizedshape of the formed pattern in the image), or with the locations of acollection of spatially distributed EPs 730 and/or of EPs 740 (e.g., bya computer image processing technique that can mathematically align thespatially distributed EPs 730 and/or of EPs 740 with the generalizedshape of the formed pattern in the image). The alignment can be doneusing die to database (D2DB) capabilities of an inspection apparatus.

To determine the location of the one or more EPs on the measured patternimage, a spatial bearing direction included in, or derived from, thespatial bearing information is used along with the location of anassociated EP on the simulated target contour and/or of an associated EPon the target polygon. In an embodiment, where the spatial bearinginformation does not include the spatial bearing direction, the spatialbearing direction can be calculated from the location of an EP on thesimulated target contour and the location of the associated EP on thetarget polygon included in the spatial bearing information.

In particular, to determine the location of the one or more EPs on themeasured pattern image, the location of the associated EP on thesimulated target contour and/or from the associated EP on the targetpolygon in the image coordinate system is determined or marked and theimage is analyzed along the spatial bearing direction from the locationof the associated EP on the simulated target contour in the imagecoordinate system and/or from the associated EP on the target polygon inthe image coordinate system to identify where along the spatial bearingdirection the boundary of the pattern is intercepted. So, in anembodiment and in the context of FIG. 7, the result is effectivelydetermining the intercept of the imaginary line 750 with the boundary ofthe measured pattern image 720 to identify the location of EP 760 on thepattern image 720 at that intersection. Of course, a line need not bedrawn on an image to accomplish identifying this intercept. Rather, adata processing technique can be applied along the direction 750 fromthe location of EP 730 in the image coordinate system and/or of EP 740in the image coordinate system to identify where the boundary of thepattern image 720 is reached. The image data processing technique toidentify the boundary can be any present or future technique for thispurpose. In an embodiment, a known measurement algorithm (e.g., CDmeasurement algorithm) and associated threshold can be used as used for,e.g., cutline gauge determination. For example, in an embodiment, theimage data processing can evaluate the gradient of the values of thepixel data and identify the boundary where the gradient crosses or meetsa certain threshold (e.g., the maximum gradient or within 10% of themaximum). This technique can enable the identification of the boundaryas a location somewhere on the up or down slope of the edge of thepattern (e.g., about the middle of the slope or a position on the slopeabout 10-30% from the bottom).

A practical example of this determination is depicted in FIG. 9. FIG. 9shows an image of a portion of a pattern. The measured boundary 920 ofthe pattern is shown along with the applicable portion of the targetpolygon 700 (which is shown for reference in this example and need notbe “drawn” on the image). In this example, the spatial bearinginformation used is the location of EP 740 (i.e., the location of an EPon the simulated target contour) along with a spatial bearing angle,which is represented in this example by imaginary line 750. While only asingle location of EP 740 is marked here for convenience, it is apparentthat FIG. 9 depicts a plurality of other locations of EPs 740 at variouspoints along the boundary 920. Further, the lines do not precisely passthrough the EPs 740 in this example merely so that the EPs 740 can bevisually seen. In practice, the spatial bearing angles will pass throughthe respective EPs 740.

Then, it can be seen that the intercept of the imaginary line 750 withthe boundary of the measured pattern image 720 identifies the locationof EP 760 on the pattern image 720 at that intersection. The pixel dataalong the imaginary line 750 can be processed to identify the locationof the edge/boundary of the pattern, which was determined in this caseas being the location where EP 760 is marked. This data processing canbe done using an algorithm such as, for example, an analysis of thegradient of the pixel data and then the location of the EP 760 beingidentified where the gradient data meets or crosses some thresholdassociated with that gradient data. So, in an embodiment, the EPlocation is determined on the image (e.g., aligned with GDS, GDSII orOASIS coordinate system) based on a reference location (e.g., EP 730and/or EP 740) and a threshold that identifies the boundary of thepattern.

In an embodiment, the identified location of EP 760 on the pattern image720 at that intersection as discussed above can represent themeasurement of the EP 760. Thus, in an embodiment, an EP location of apattern on a substrate can be directly determined from an image (e.g.,after alignment with the target polygon and/or the simulated targetcontour such as by alignment with GDS, GDSII or OASIS coordinate system)based on a certain measurement method (e.g., a known measurementalgorithm (e.g., CD measurement algorithm) and associated threshold usedfor, e.g., cutline gauge determination).

In an embodiment, the location of the EP 760 on a contour of the patternimage 720 can be the measurement of the EP 760. For example, in anembodiment, a contour of the image can be obtained at or near theidentified location of EP 760 on the pattern image 720 and themeasurement of EP 760 is the location of EP 760 on the contour. In anembodiment, the contour of the image does not encompass the entireboundary of the pattern. In an embodiment, the contour is obtained so asto include the identified location of EP 760 on the pattern image 720 soas to be able to avoid interpolation.

As will be appreciated, this analysis can be performed with respect toall the EPs 740 (using their respective spatial bearing information)along the boundary of the pattern to obtain the values of themeasurements of EPs 760 along the perimeter of the pattern 720. Ofcourse, the locations of EPs 740, the imaginary lines 750 and/or thelocations of EPs 760 need not be “drawn” on the image. Rather, the imagedata can be mathematically processed to achieve the same effect.

Optionally, a distance between the location of an EP 740 and ameasurement of its associated EP 760 can be determined. In anembodiment, the distance is the Euclidean distance between the locationof EP 740 and the measurement of EP 760. In an embodiment, this distancerepresents an edge placement error (EPE).

Optionally, referring to FIG. 10, an “averaged” determination of thelocation of EP 760 can be obtained. FIG. 10 shows a portion of theboundary of a pattern image 720 for a plurality of different instancesof the same pattern. In an embodiment, the pattern can be a contact holepattern and so the plurality of instances can be various instances ofthe contact hole pattern formed on a substrate.

In an embodiment, the “averaged” determination of the location of EP 760can be obtained by determining the location of the evaluation point onthe measured image of the at least part of the pattern for each of aplurality of different instances of the at least part of the pattern.Then, the location can be based on a mathematical combination of thedetermined locations (e.g., an average of the locations). For example,as shown in FIG. 10, the imaginary line 750 extends relative to thelocation of an EP 740 defined with respect to a simulated contour of thepattern. The imaginary line 750 intercepts a plurality of instances of apattern image 720 at various locations of EP 760. In an embodiment,those determined locations of EP 760 can be mathematically combined toyield a single value of the location for EP 760. In an embodiment, thatcombination can be an average or other statistical combination.

In an embodiment, the “averaged” determination of the location of EP 760can be obtained by combination of the images of the different instancesof the at least part of the pattern into a “single” image of the atleast part of the pattern. The location of EP 760 can then be determinedfrom that combination image using, e.g., an imaginary line 750 extendingrelative to the location of an EP 740 defined with respect to asimulated contour of the pattern.

Of course, that identified location of EP 760 can represent themeasurement of the EP 760 or the location of the EP 760 on a contour ofthe pattern image 720 can be the measurement of the EP 760. Of course, adistance between the location of an EP 740 and a measurement of itsassociated EP 760 can be determined using the “averaged” determinationof the location of EP 760.

At 850, EP spatial parameter information is output. In an embodiment,the EP spatial parameter information is electronic informationcomprising values for the one or more EPs analyzed. In an embodiment,the EP spatial parameter information comprises the measurement of one ormore locations of EPs 760. In an embodiment, the one or more locationscan be Cartesian coordinates in, for example, the coordinate system ofthe image or some other coordinate system. In an embodiment, the EPspatial parameter information comprises the distance between one or moreEP 740 locations and a measurement of its associated one or more EPs760. In an embodiment, the EP spatial parameter information can be basedon an “averaged” determination as discussed above.

At 860, the EP spatial parameter information can be used for processmodeling, model calibration (including recalibration), defect detection,estimation, characterization or classification, yield estimation,process control or monitoring, patterning process design, etc.

So, this EP technique can enable faster determination of EP data by, forexample, reducing the data analysis time. For example, the measurementand analysis can be done in near real-time.

Additionally or alternatively, in an embodiment, the results can bealready mapped with GDS, GDSII and/or OASIS reference points where, forexample, the image is so aligned. This can facilitate, e.g., modelcalibration where, for example, the model is aligned with such acoordinate system.

Additionally or alternatively, the EP technique can avoid some or allcontour extraction from an image, which contour extraction can introduceartifacts and/or errors.

Additionally or alternatively, the EP technique can avoid or reduce thenumber of images frames of the pattern taken with electron beamirradiation and thus improve the quality of the results. This is becauseextra frames introduce damage to the pattern and which damages ismeasured in the subsequent image frames.

Additionally or alternatively, the EP technique can reduce the number ofsampling points and/or reduce the need for interpolation, since selectEP locations can be used and determined.

Therefore, the EP technique can help avoid contour extraction (and anassociated large contour data file), reduce computational time and/orreduce EP positional error due to, for example, artifacts/errors incontour extraction and/or from interpolation.

In an embodiment, there is provided a method comprising: obtaining asimulation of a contour of a pattern to be formed on a substrate using apatterning process; determining, by a hardware computer system, alocation of an evaluation point on the simulated contour of the pattern,the location spatially associated with a location of a correspondingevaluation point on a design layout for the pattern; and producing, bythe hardware computer system, electronic information corresponding to aspatial bearing between the location of the evaluation point on thesimulated contour and the location of the corresponding evaluation pointon the design layout, wherein the information corresponding to thespatial bearing is configured for determining a location of anevaluation point on a measured image of at least part of the pattern,the evaluation point on the measured image spatially associated with thecorresponding evaluation point on the design layout.

In an embodiment, the location of the evaluation point on the simulatedcontour of the pattern is spatially associated with the location of thecorresponding evaluation point on the design layout by the location ofthe evaluation point on the simulated contour of the pattern being thelocation on the simulated contour that is the substantially shortestdistance between the contour and the location of the correspondingevaluation point on the design layout. In an embodiment, the informationcorresponding to the spatial bearing comprises the location of theevaluation point on the simulated contour of the pattern and/or of thecorresponding evaluation point on the design layout and a directionbetween the locations of the evaluation point on the simulated contourof the pattern and the corresponding evaluation point on the designlayout. In an embodiment, the direction comprises an angle or slope. Inan embodiment, the information corresponding to the spatial bearingcomprises a location of the evaluation point on the simulated contour ofthe pattern and of the corresponding evaluation point on the designlayout. In an embodiment, the method further comprises: obtaining ameasured image of at least part of the pattern formed on a substrate;determining, based on the spatial bearing information, the location ofthe evaluation point on the measured image of at least part of thepattern, the evaluation point on the measured image spatially associatedwith the corresponding evaluation point on the design layout; andoutputting spatial parameter information based on the determinedlocation. In an embodiment, the method further comprises determining adistance between the location of the evaluation point on the simulatedcontour of the pattern and a measurement associated with the evaluationpoint on the measured image of the at least part of the pattern andwherein the spatial parameter information comprises the determineddistance. In an embodiment, the method further comprises performing acalibration of a mathematical model representing at least part of thepatterning process based on the spatial parameter information. In anembodiment, the method further comprises performing a computersimulation to produce the simulated contour of the pattern.

In an embodiment, there is provided a method comprising: obtainingelectronic information corresponding to a spatial bearing between alocation of an evaluation point on a simulated contour of a pattern tobe formed on a substrate using a patterning process and a location of acorresponding evaluation point on a design layout for the pattern;obtaining a measured image of at least part of the pattern; determining,by a hardware computer system and based on the spatial bearinginformation, a location of an evaluation point on the measured image ofthe at least part of the pattern, the evaluation point on the measuredimage spatially associated with the corresponding evaluation point onthe design layout; and outputting spatial parameter information based onthe determined location.

In an embodiment, the location of the evaluation point on the simulatedcontour of the pattern is the location on the simulated contour that isthe substantially shortest distance between the contour and the locationof the corresponding evaluation point on the design layout. In anembodiment, the information corresponding to the spatial bearingcomprises the location of the evaluation point on the simulated contourof the pattern and/or of the corresponding evaluation point on thedesign layout and a direction between the locations of the evaluationpoint on the simulated contour of the pattern and the correspondingevaluation point on the design layout. In an embodiment, the directioncomprises an angle or slope. In an embodiment, the informationcorresponding to the spatial bearing comprises a location of theevaluation point on the simulated contour of the pattern and of thecorresponding evaluation point on the design layout. In an embodiment,the method further comprises determining a distance between the locationof the evaluation point on the simulated contour of the pattern and ameasurement associated with the evaluation point on the measured imageof the at least part of the pattern and wherein the spatial parameterinformation comprises the determined distance. In an embodiment, themethod further comprises performing a computer simulation to produce thesimulated contour of the pattern. In an embodiment, the method furthercomprises performing a calibration of a mathematical model representingat least part of the patterning process based on the spatial parameterinformation. In an embodiment, the location of the evaluation point onthe measured image of the at least part of the pattern is determined fora plurality of different instances of the at least part of the patternand the spatial parameter information is based on a mathematicalcombination of the determined locations, or wherein the measured imageof the at least part of the pattern is a combination of images ofdifferent instances of the at least part of the pattern.

An embodiment may include a computer program containing one or moresequences of machine-readable instructions that enable practice of amethod as described herein. This computer program may be included, forexample, with or within the apparatus of any of FIGS. 1-4. There mayalso be provided a data storage medium (e.g., semiconductor memory,magnetic or optical disk) having such a computer program stored therein.Where an existing apparatus, for example of the type shown in any FIGS.1-4, is already in production and/or in use, an embodiment can beimplemented by the provision of updated computer program products forcausing a processor of the apparatus to perform a method as describedherein.

The embodiments may further be described using the following clauses:

-   1. A method comprising:

obtaining a simulation of a contour of a pattern to be formed on asubstrate using a patterning process;

determining, by a hardware computer system, a location of an evaluationpoint on the simulated contour of the pattern, the location spatiallyassociated with a location of a corresponding evaluation point on adesign layout for the pattern; and

producing, by the hardware computer system, electronic informationcorresponding to a spatial bearing between the location of theevaluation point on the simulated contour and the location of thecorresponding evaluation point on the design layout, wherein theinformation corresponding to the spatial bearing is configured fordetermining a location of an evaluation point on a measured image of atleast part of the pattern, the evaluation point on the measured imagespatially associated with the corresponding evaluation point on thedesign layout.

-   2. The method of clause 1, wherein the location of the evaluation    point on the simulated contour of the pattern is spatially    associated with the location of the corresponding evaluation point    on the design layout by the location of the evaluation point on the    simulated contour of the pattern being the location on the simulated    contour that is the substantially shortest distance between the    contour and the location of the corresponding evaluation point on    the design layout.-   3. The method of clause 1 or clause 2, wherein the information    corresponding to the spatial bearing comprises the location of the    evaluation point on the simulated contour of the pattern and/or of    the corresponding evaluation point on the design layout and a    direction between the locations of the evaluation point on the    simulated contour of the pattern and the corresponding evaluation    point on the design layout.-   4. The method of clause 4, wherein the direction comprises an angle    or slope.-   5. The method of any of clauses 1-4, wherein the information    corresponding to the spatial bearing comprises a location of the    evaluation point on the simulated contour of the pattern and of the    corresponding evaluation point on the design layout.-   6. The method of any of clauses 1-5, further comprising:

obtaining a measured image of at least part of the pattern formed on asubstrate; determining, based on the spatial bearing information, thelocation of the evaluation point on the measured image of at least partof the pattern, the evaluation point on the measured image spatiallyassociated with the corresponding evaluation point on the design layout;and outputting spatial parameter information based on the determinedlocation.

-   7. The method of clause 6, further comprising determining a distance    between the location of the evaluation point on the simulated    contour of the pattern and a measurement associated with the    evaluation point on the measured image of the at least part of the    pattern and wherein the spatial parameter information comprises the    determined distance.-   8. The method of clause 6 or clause 7, further comprising performing    a calibration of a mathematical model representing at least part of    the patterning process based on the spatial parameter information.-   9. The method of any of clauses 1-8, further comprising performing a    computer simulation to produce the simulated contour of the pattern.-   10. A method comprising:

obtaining electronic information corresponding to a spatial bearingbetween a location of an evaluation point on a simulated contour of apattern to be formed on a substrate using a patterning process and alocation of a corresponding evaluation point on a design layout for thepattern; obtaining a measured image of at least part of the pattern;

-   determining, by a hardware computer system and based on the spatial    bearing information, a location of an evaluation point on the    measured image of the at least part of the pattern, the evaluation    point on the measured image spatially associated with the    corresponding evaluation point on the design layout; and-   outputting spatial parameter information based on the determined    location.-   11. The method of clause 10, wherein the location of the evaluation    point on the simulated contour of the pattern is the location on the    simulated contour that is the substantially shortest distance    between the contour and the location of the corresponding evaluation    point on the design layout.-   12. The method of clause 10 or clause 11, wherein the information    corresponding to the spatial bearing comprises the location of the    evaluation point on the simulated contour of the pattern and/or of    the corresponding evaluation point on the design layout and a    direction between the locations of the evaluation point on the    simulated contour of the pattern and the corresponding evaluation    point on the design layout.-   13. The method of clause 12, wherein the direction comprises an    angle or slope.-   14. The method of any of clauses 10-13, wherein the information    corresponding to the spatial bearing comprises a location of the    evaluation point on the simulated contour of the pattern and of the    corresponding evaluation point on the design layout.-   15. The method of any of clauses 10-14, further comprising    determining a distance between the location of the evaluation point    on the simulated contour of the pattern and a measurement associated    with the evaluation point on the measured image of the at least part    of the pattern and wherein the spatial parameter information    comprises the determined distance.-   16. The method of any of clauses 10-15, further comprising    performing a computer simulation to produce the simulated contour of    the pattern.-   17. The method of any of clauses 10-16, further comprising    performing a calibration of a mathematical model representing at    least part of the patterning process based on the spatial parameter    information.-   18. The method of any of clauses 10-17, wherein the location of the    evaluation point on the measured image of the at least part of the    pattern is determined for a plurality of different instances of the    at least part of the pattern and the spatial parameter information    is based on a mathematical combination of the determined locations,    or-   wherein the measured image of the at least part of the pattern is a    combination of images of different instances of the at least part of    the pattern.-   19. A method of manufacturing devices wherein a device pattern is    applied to a series of substrates using a patterning process, the    method including evaluating a patterned structure formed using the    patterning process using the method of any of clauses 1-18 and    controlling the patterning process for one or more of the substrates    in accordance with a result of the method.-   20. A non-transitory computer program product comprising    machine-readable instructions configured to cause a processor to    cause performance of the method of any of clauses 1-19.-   21. An inspection system, comprising:

an inspection apparatus; and

an analysis engine comprising the non-transitory computer programproduct of clause 20.

-   22. The system of clause 21, wherein the inspection apparatus    comprises an electron beam inspection apparatus.-   23. The system of clause 21 or clause 22, further comprising a    lithographic apparatus comprising a support structure configured to    hold a patterning device to modulate a radiation beam and a    projection optical system arranged to project the modulated    radiation beam onto a radiation-sensitive substrate.

An embodiment of the invention may take the form of a computer programcontaining one or more sequences of machine-readable instructions tocause execution of a method as disclosed herein, or a data storagemedium (e.g. semiconductor memory, magnetic or optical disk) having sucha computer program stored therein. Further, the machine readableinstruction may be embodied in two or more computer programs. The two ormore computer programs may be stored on one or more different memoriesand/or data storage media.

Any controllers described herein may each or in combination be operablewhen the one or more computer programs are read by one or more computerprocessors located within at least one component of the lithographicapparatus. The controllers may each or in combination have any suitableconfiguration for receiving, processing, and sending signals. One ormore processors are configured to communicate with the at least one ofthe controllers. For example, each controller may include one or moreprocessors for executing the computer programs that includemachine-readable instructions for the methods described above. Thecontrollers may include data storage medium for storing such computerprograms, and/or hardware to receive such medium. So the controller(s)may operate according the machine readable instructions of one or morecomputer programs.

Although specific reference may have been made above to the use ofembodiments in the context of optical lithography, it will beappreciated that an embodiment of the invention may be used in otherapplications, for example imprint lithography, and where the contextallows, is not limited to optical lithography. In imprint lithography, atopography in a patterning device defines the pattern created on asubstrate. The topography of the patterning device may be pressed into alayer of resist supplied to the substrate whereupon the resist is curedby applying electromagnetic radiation, heat, pressure or a combinationthereof. The patterning device is moved out of the resist leaving apattern in it after the resist is cured.

Although specific reference may be made in this text to the manufactureof ICs, it should be understood that the description herein has manyother possible applications. For example, it may be employed in themanufacture of integrated optical systems, guidance and detectionpatterns for magnetic domain memories, flat-panel displays,micro-electro mechanical systems (MEMS), liquid-crystal display panels,thin-film magnetic heads, etc. The skilled artisan will appreciate that,in the context of such alternative applications, any use of the terms“reticle”, “wafer” or “die” in this text should be considered asinterchangeable with the more general terms “mask”, “substrate” and“target portion”, respectively.

The substrate referred to herein may be processed, before or afterexposure, in for example a track (a tool that typically applies a layerof resist to a substrate and develops the exposed resist), a metrologytool and/or an inspection tool. Where applicable, the disclosure hereinmay be applied to such and other substrate processing tools. Further,the substrate may be processed more than once, for example in order tocreate a multi-layer IC, so that the term substrate used herein may alsorefer to a substrate that already contains multiple processed layers.

Unless specifically noted otherwise, the terms “radiation” and “beam”used herein encompass all types of electromagnetic radiation, includingultraviolet (UV) radiation (e.g. having a wavelength of or about 365,355, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation(e.g. having a wavelength in the range of 5-20 nm), as well as particlebeams, such as ion beams or electron beams.

It is noted that the terms “mask”, “reticle”, “patterning device” areutilized interchangeably herein. Also, a person skilled in the art willrecognize that, especially in the context of lithographysimulation/optimization, the term “mask”/“patterning device” and “designlayout” can be used interchangeably, as in lithographysimulation/optimization, that a physical patterning device is notnecessarily used but a design layout can be used to represent a physicalpatterning device.

The term “projection optics” as used herein should be broadlyinterpreted as encompassing various types of optical systems, includingrefractive optics, reflective optics, apertures and catadioptric optics,for example. The term “projection optics” may also include componentsoperating according to any of these design types for directing, shapingor controlling the projection beam of radiation, collectively orsingularly. The term “projection optics” may include any opticalcomponent in the lithographic projection apparatus, no matter where theoptical component is located on an optical path of the lithographicprojection apparatus. Projection optics may include optical componentsfor shaping, adjusting and/or projecting radiation from the sourcebefore the radiation passes the patterning device, and/or opticalcomponents for shaping, adjusting and/or projecting the radiation afterthe radiation passes the patterning device. The projection opticsgenerally exclude the source and the patterning device.

In an optimization process of a system or process, a figure of merit ofthe system or process can be represented as a cost function. Theoptimization process boils down to a process of finding a set ofparameters (design variables) of the system or process that optimizes(e.g., minimizes or maximizes) the cost function. The cost function canhave any suitable form depending on the goal of the optimization. Forexample, the cost function can be weighted root mean square (RMS) ofdeviations of certain characteristics (evaluation points) of the systemor process with respect to the intended values (e.g., ideal values) ofthese characteristics; the cost function can also be the maximum ofthese deviations (i.e., worst deviation). The term “evaluation points”herein should be interpreted broadly to include any characteristics ofthe system or process. The design variables of the system or process canbe confined to finite ranges and/or be interdependent due topracticalities of implementations of the system or process. In the caseof a lithographic apparatus or patterning process, the constraints areoften associated with physical properties and characteristics of thehardware such as tunable ranges, and/or patterning devicemanufacturability design rules, and the evaluation points can includephysical points on a resist image or pattern on a substrate, as well asnon-physical characteristics such as dose and focus.

The term “optimizing” and “optimization” as used herein refers to ormeans adjusting a patterning process apparatus, one or more steps of apatterning process, etc. such that results and/or processes ofpatterning have more desirable characteristics, such as higher accuracyof transfer of a design layout on a substrate, a larger process window,etc. Thus, the term “optimizing” and “optimization” as used hereinrefers to or means a process that identifies one or more values for oneor more parameters that provide an improvement, e.g. a local optimum, inat least one relevant metric, compared to an initial set of one or morevalues for those one or more parameters. “Optimum” and other relatedterms should be construed accordingly. In an embodiment, optimizationsteps can be applied iteratively to provide further improvements in oneor more metrics.

In block diagrams, illustrated components are depicted as discretefunctional blocks, but embodiments are not limited to systems in whichthe functionality described herein is organized as illustrated. Thefunctionality provided by each of the components may be provided bysoftware or hardware modules that are differently organized than ispresently depicted, for example such software or hardware may beintermingled, conjoined, replicated, broken up, distributed (e.g. withina data center or geographically), or otherwise differently organized Thefunctionality described herein may be provided by one or more processorsof one or more computers executing code stored on a tangible,non-transitory, machine readable medium. In some cases, third partycontent delivery networks may host some or all of the informationconveyed over networks, in which case, to the extent information (e.g.,content) is said to be supplied or otherwise provided, the informationmay be provided by sending instructions to retrieve that informationfrom a content delivery network.

Unless specifically stated otherwise, as apparent from the discussion,it is appreciated that throughout this specification discussionsutilizing terms such as “processing,” “computing,” “calculating,”“determining” or the like refer to actions or processes of a specificapparatus, such as a special purpose computer or a similar specialpurpose electronic processing/computing device.

The reader should appreciate that the present application describesseveral inventions. Rather than separating those inventions intomultiple isolated patent applications, applicants have grouped theseinventions into a single document because their related subject matterlends itself to economies in the application process. But the distinctadvantages and aspects of such inventions should not be conflated. Insome cases, embodiments address all of the deficiencies noted herein,but it should be understood that the inventions are independentlyuseful, and some embodiments address only a subset of such problems oroffer other, unmentioned benefits that will be apparent to those ofskill in the art reviewing the present disclosure. Due to costsconstraints, some inventions disclosed herein may not be presentlyclaimed and may be claimed in later filings, such as continuationapplications or by amending the present claims. Similarly, due to spaceconstraints, neither the Abstract nor the Summary of the Inventionsections of the present document should be taken as containing acomprehensive listing of all such inventions or all aspects of suchinventions.

It should be understood that the description and the drawings are notintended to limit the invention to the particular form disclosed, but tothe contrary, the intention is to cover all modifications, equivalents,and alternatives falling within the spirit and scope of the presentinvention as defined by the appended claims.

Modifications and alternative embodiments of various aspects of theinvention will be apparent to those skilled in the art in view of thisdescription. Accordingly, this description and the drawings are to beconstrued as illustrative only and are for the purpose of teaching thoseskilled in the art the general manner of carrying out the invention. Itis to be understood that the forms of the invention shown and describedherein are to be taken as examples of embodiments. Elements andmaterials may be substituted for those illustrated and described herein,parts and processes may be reversed or omitted, certain features may beutilized independently, and embodiments or features of embodiments maybe combined, all as would be apparent to one skilled in the art afterhaving the benefit of this description of the invention. Changes may bemade in the elements described herein without departing from the spiritand scope of the invention as described in the following claims.Headings used herein are for organizational purposes only and are notmeant to be used to limit the scope of the description.

As used throughout this application, the word “may” is used in apermissive sense (i.e., meaning having the potential to), rather thanthe mandatory sense (i.e., meaning must). The words “include”,“including”, and “includes” and the like mean including, but not limitedto. As used throughout this application, the singular forms “a,” “an,”and “the” include plural referents unless the content explicitlyindicates otherwise. Thus, for example, reference to “an” element or “a”element includes a combination of two or more elements, notwithstandinguse of other terms and phrases for one or more elements, such as “one ormore.” The term “or” is, unless indicated otherwise, non-exclusive,i.e., encompassing both “and” and “or.” Terms describing conditionalrelationships, e.g., “in response to X, Y,” “upon X, Y,”, “if X, Y,”“when X, Y,” and the like, encompass causal relationships in which theantecedent is a necessary causal condition, the antecedent is asufficient causal condition, or the antecedent is a contributory causalcondition of the consequent, e.g., “state X occurs upon condition Yobtaining” is generic to “X occurs solely upon Y” and “X occurs upon Yand Z.” Such conditional relationships are not limited to consequencesthat instantly follow the antecedent obtaining, as some consequences maybe delayed, and in conditional statements, antecedents are connected totheir consequents, e.g., the antecedent is relevant to the likelihood ofthe consequent occurring. Statements in which a plurality of attributesor functions are mapped to a plurality of objects (e.g., one or moreprocessors performing steps A, B, C, and D) encompasses both all suchattributes or functions being mapped to all such objects and subsets ofthe attributes or functions being mapped to subsets of the attributes orfunctions (e.g., both all processors each performing steps A-D, and acase in which processor 1 performs step A, processor 2 performs step Band part of step C, and processor 3 performs part of step C and step D),unless otherwise indicated. Further, unless otherwise indicated,statements that one value or action is “based on” another condition orvalue encompass both instances in which the condition or value is thesole factor and instances in which the condition or value is one factoramong a plurality of factors. Unless otherwise indicated, statementsthat “each” instance of some collection have some property should not beread to exclude cases where some otherwise identical or similar membersof a larger collection do not have the property, i.e., each does notnecessarily mean each and every.

To the extent certain U.S. patents, U.S. patent applications, or othermaterials (e.g., articles) have been incorporated by reference, the textof such U.S. patents, U.S. patent applications, and other materials isonly incorporated by reference to the extent that no conflict existsbetween such material and the statements and drawings set forth herein.In the event of such conflict, any such conflicting text in suchincorporated by reference U.S. patents, U.S. patent applications, andother materials is specifically not incorporated by reference herein.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below. For example, one or more aspects ofone or more embodiments may be combined with or substituted for one ormore aspects of one or more other embodiments as appropriate. Therefore,such adaptations and modifications are intended to be within the meaningand range of equivalents of the disclosed embodiments, based on theteaching and guidance presented herein. It is to be understood that thephraseology or terminology herein is for the purpose of description byexample, and not of limitation, such that the terminology or phraseologyof the present specification is to be interpreted by the skilled artisanin light of the teachings and guidance. The breadth and scope of theinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

1. A method comprising: obtaining a simulation of a contour of a patternto be formed on a substrate using a patterning process; determining, bya hardware computer system, a location of an evaluation point on thesimulated contour of the pattern, the location spatially associated witha location of a corresponding evaluation point on a design layout forthe pattern; and producing, by the hardware computer system, electronicinformation corresponding to a spatial bearing between the location ofthe evaluation point on the simulated contour and the location of thecorresponding evaluation point on the design layout, wherein theinformation corresponding to the spatial bearing is configured fordetermining a location of an evaluation point on a measured image of atleast part of the pattern, the evaluation point on the measured imagespatially associated with the corresponding evaluation point on thedesign layout.
 2. The method of claim 1, wherein the location of theevaluation point on the simulated contour of the pattern is spatiallyassociated with the location of the corresponding evaluation point onthe design layout by the location of the evaluation point on thesimulated contour of the pattern being the location on the simulatedcontour that is the substantially shortest distance between the contourand the location of the corresponding evaluation point on the designlayout.
 3. The method of claim 1, wherein the information correspondingto the spatial bearing comprises the location of the evaluation point onthe simulated contour of the pattern and/or of the correspondingevaluation point on the design layout and a direction between thelocations of the evaluation point on the simulated contour of thepattern and the corresponding evaluation point on the design layout. 4.The method of claim 3, wherein the direction comprises an angle orslope.
 5. The method of claim 1, wherein the information correspondingto the spatial bearing comprises a location of the evaluation point onthe simulated contour of the pattern and of the corresponding evaluationpoint on the design layout.
 6. The method of claim 1, furthercomprising: obtaining a measured image of at least part of the patternformed on a substrate; determining, based on the spatial bearinginformation, the location of the evaluation point on the measured imageof at least part of the pattern, the evaluation point on the measuredimage spatially associated with the corresponding evaluation point onthe design layout; and outputting spatial parameter information based onthe determined location.
 7. The method of claim 6, further comprisingdetermining a distance between the location of the evaluation point onthe simulated contour of the pattern and a measurement associated withthe evaluation point on the measured image of the at least part of thepattern and wherein the spatial parameter information comprises thedetermined distance.
 8. The method of claim 6, further comprisingperforming a calibration of a mathematical model representing at leastpart of the patterning process based on the spatial parameterinformation.
 9. The method of claim 1, further comprising performing acomputer simulation to produce the simulated contour of the pattern. 10.(canceled)
 11. The method of claim 1, further comprising evaluating thepattern formed on the substrate and controlling the patterning processin accordance with a result of the method.
 12. A non-transitory computerprogram product comprising machine-readable instructions therein, theinstructions, upon execution by a processor system, configured to causethe processor system to cause performance of at least: obtain asimulation of a contour of a pattern to be formed on a substrate using apatterning process; determine a location of an evaluation point on thesimulated contour of the pattern, the location spatially associated witha location of a corresponding evaluation point on a design layout forthe pattern; and produce electronic information corresponding to aspatial bearing between the location of the evaluation point on thesimulated contour and the location of the corresponding evaluation pointon the design layout, wherein the information corresponding to thespatial bearing is configured for determining a location of anevaluation point on a measured image of at least part of the pattern,the evaluation point on the measured image spatially associated with thecorresponding evaluation point on the design layout.
 13. An inspectionsystem, comprising: an inspection apparatus; and an analysis enginecomprising the non-transitory computer program product of claim
 12. 14.The system of claim 13, wherein the inspection apparatus comprises anelectron beam inspection apparatus.
 15. The system of claim 13, furthercomprising a lithographic apparatus comprising a support structureconfigured to hold a patterning device to modulate a radiation beam anda projection optical system arranged to project the modulated radiationbeam onto a radiation-sensitive substrate.
 16. A method comprising:obtaining electronic information corresponding to a spatial bearingbetween a location of an evaluation point on a simulated contour of apattern to be formed on a substrate using a patterning process and alocation of a corresponding evaluation point on a design layout for thepattern; obtaining a measured image of at least part of the pattern;determining, by a hardware computer system and based on the spatialbearing information, a location of an evaluation point on the measuredimage of the at least part of the pattern, the evaluation point on themeasured image spatially associated with the corresponding evaluationpoint on the design layout; and outputting spatial parameter informationbased on the determined location.
 17. The method of claim 16, whereinthe location of the evaluation point on the simulated contour of thepattern is the location on the simulated contour that is thesubstantially shortest distance between the contour and the location ofthe corresponding evaluation point on the design layout.
 18. The methodof claim 16, wherein the information corresponding to the spatialbearing comprises the location of the evaluation point on the simulatedcontour of the pattern and/or of the corresponding evaluation point onthe design layout and a direction between the locations of theevaluation point on the simulated contour of the pattern and thecorresponding evaluation point on the design layout.
 19. The method ofclaim 16, wherein the information corresponding to the spatial bearingcomprises a location of the evaluation point on the simulated contour ofthe pattern and of the corresponding evaluation point on the designlayout.
 20. The method of claim 16, wherein the location of theevaluation point on the measured image of the at least part of thepattern is determined for a plurality of different instances of the atleast part of the pattern and the spatial parameter information is basedon a mathematical combination of the determined locations, or whereinthe measured image of the at least part of the pattern is a combinationof images of different instances of the at least part of the pattern.21. A non-transitory computer program product comprisingmachine-readable instructions therein, the instructions, upon executionby a processor system, configured to cause the processor system to causeperformance of the method of claim 16.